The present application claims priority to Japanese Application(s) No(s). P2000-394339 filed Dec. 26, 2000, which application(s) is/are incorporated herein by reference to the extent permitted by law.
The present invention relates to an etching method for forming a fine structure in a plastic substrate.
Plastic working has been generally performed by a molding technique using a mold, or a physically cutting technique which makes use of cutting, etching, or sandblast. According to such a plastic working technique, for example, a plastic substrate can be formed into a desired shape.
The above-described related art plastic working technique, however, has a problem that it is difficult to accurately work a plastic substrate. The reason for this is as follows: namely, for example, in the case of forming a fine structure such as a recess, which has a circular opening shape of an inner diameter of 1.0 mm or less, in a plastic substrate, there occurs a variation in inner diameter of the recess in the depth direction because the working accuracy of the related art plastic working technique is insufficient to form a fine structure. This becomes significant, particularly, in the case of forming a fine recess having a depth being twice or more an inner diameter.
An object of the present invention is to provide an etching method capable of accurately forming a fine structure in a plastic substrate.
To achieve the above object, according to an aspect of the present invention, there is provided an etching method including: a first step of subjecting a plastic substrate to ion implantation treatment, to reform a surface of the plastic substrate, thereby forming a surface reformed layer; and a second step of subjecting the plastic substrate to wet etching treatment using a specific etchant by determining an end point of the wet etching treatment with the use of the surface reformed layer.
With this configuration, at the time of wet etching treatment, an etching range can be controlled by the surface reformed layer. Accordingly, unlike the related art plastic working using a molding technique or a cutting technique, a fine structure can be accurately formed in a plastic substrate. Further, since an etching direction (anisotropic or isotropic direction) at the time of wet etching treatment can be controlled, various kinds of micro-machines can be each formed by using such a plastic substrate having a fine structure.
In this method, preferably, a solution, which can dissolve a layer to be etched in the second step and cannot dissolve the surface reformed layer, is used as the etchant, or a solution, which has a high selection ratio of etching of a layer to be etched in the second step at least to etching of the surface reformed layer, is used as the etchant.
Preferably, limonene is used as the etchant. With this configuration, it is possible to shorten a time required for etching, and to eliminate a problem associated with an environmental contamination of waste of the etchant.
Preferably, the second step is carried out in an ultrasonic environment.
Preferably, the etching method further includes a third step of forming a specific thin film on the surface reformed layer, the third step being inserted between the first step and the second step.
With this configuration, it is possible to obtain a plastic substrate in which a fine structure provided with a specific thin film is accurately formed.